Extinction Selectivity Research Articles

Selectivity of foraminiferal extinction in the late Eocene

Late Eocene foraminiferal extinction shows diverse patterns of selective morphologic and latitudinal extinction. Taxa with discoidal shape, calcareous tests, and narrow and low-latitudinal ranges are at significantly greater risk of extinction. Elevated extinction intensities in calcareous tests are mainly due to the presence of larger benthic foraminifera that evolved in late Paleocene and diversified through the lower to middle Eocene. Selectivity of late Eocene foraminiferal extinction indicates that this extinction event was not a globally uniform event. Although this result does not verify an extraterrestrial impact or any other proposed cause of extinction, it does constrain the causes of late Eocene extinction. Furthermore, the geography of late Eocene foraminiferal extinction, and previously studied Cenomanian/Turonian extinction, demonstrates that mass extinctions exhibit different patterns of selectivity.

Comparative Earth History and Late Permian Mass Extinction

The repeated association during the late Neoproterozoic Era of large carbon-isotopic excursions, continental glaciation, and stratigraphically anomalous carbonate precipitation provides a framework for interpreting the reprise of these conditions on the Late Permian Earth. A paleoceanographic model that was developed to explain these stratigraphically linked phenomena suggests that the overturn of anoxic deep oceans during the Late Permian introduced high concentrations of carbon dioxide into surficial environments. The predicted physiological and climatic consequences for marine and terrestrial organisms are in good accord with the observed timing and selectivity of Late Permian mass extinction.

Extinction selectivity and ecology of Neogene Caribbean reef corals

We analyze a new compilation of Neogene to Recent (22-0 Ma) Caribbean coral occurrences to determine how ecological and life history traits at the population level affect long-term evolutionary patterns. The compilation consists of occurrences of 175 species and 49 genera in one continuous (> 5 m.y.) sequence and 22 scattered sites across the Caribbean region. Previous study of evolutionary rates using these data has shown that both extinction and origination were accelerated between 4 and 1 Ma, resulting in large-scale faunal turnover. Categories for three morphological and two reproductive variables (colony size, colony shape, and corallite size; and sex, and mode of embryonic development; respectively) are assigned to each species in the compilation. Comparisons of the ecological variables with evolutionary rates using randomization procedures and modified analysis of variance show that only colony size was strongly related to rates of extinction and origination during either normal background times or times of accelerated extinction. Extinction rates were lower in species with large colonies, because species with small massive colonies tend to live in small, short-lived populations with highly fluctuating recruitment rates. During turnover, extinction rates increased disproportionately in species with small colonies. Origination rates are found to be less related to ecological variables, although species with small massive colonies originated at higher rates prior to turnover.Accelerated turnover may have therefore involved an increase in local population extinction rates that caused increased rates of both species extinction and origination across the entire fauna. Since extinction rates accelerated disproportionately with respect to colony size, the overall result was a relative increase in species with large colonies. After severe disturbance, one might expect that populations of species with large colonies and high rates of fragmentation would be more likely to escape extinction, because of larger population sizes, longer generation times, and more constant rates of population increase. The modern Caribbean reef-coral fauna is therefore structured by large, long-lived colonies that are robust to regional environmental change. Many of the very taxa that allowed reef communities to escape collapse in the past are declining today in response to anthropogenic disturbances, suggesting that Caribbean reef communities may be less resilient in the future in response to ongoing environmental perturbations.

Extinction selectivity among lower taxa: gradational patterns and rarefaction error in extinction estimates

Documenting past environmental disturbances will provide a very incomplete explanation of extinctions until more data on intrinsic (e.g., phylogenetic) responses to disturbances are collected. Taxonomic selectivity can be used to infer phylogenetic inheritance of extinction-biasing traits. Selectivity patterns among higher taxa, such as between mammals and bivalves, are well documented. Selectivity patterns among lower taxa (genus, species) have great potential for understanding the dynamics underlying higher taxic turnover. Two echinoid data sets, of fossil and living taxa, indicate that species extinctions do not occur randomly within genera. Reverse rarefaction estimates of past species extinction rates assume random species extinction within higher taxa, so these widely cited extinction estimates may be inaccurate. Revised estimates based on a simulated curve imply that past species extinctions rates may be 6%–15% lower than previously cited. Possible causes for the observed selectivity patterns are discussed. These include nonrandom phylogenetic nesting of species with traits often cited as enhancing extinction vulnerability, into certain taxa. Such traits include low abundance, large body size, narrow niche breadth, and many others. Phylogenetic nesting of extinction-biasing traits at many taxonomic levels does not predict that a dichotomy of mass-background selectivity based on a few traits will occur. Instead, it predicts patterns of selectivity at many taxonomic levels, and at many spatio-temporal scales.

Extinction: bad genes or bad luck?

Part 1 Almost all species are extinct: is extinction important? bad genes or bad luck? the nature of extinction who studies extinction? a word about the word species defined the purpose of extinction, if any. Part 2 A brief history of life: origin of life complex life the quality of the fossil record 600 million years of fussing a stock market analogy trilobite eyes tropical reefs flying reptiles human evolution living fossils. Part 3 Gambler's ruin and other problems: gambling concepts of randomness gambling for survival differing extinction and speciation rates skewed histograms other models a note on extinction of surnames. Part 4 Mass extinctions: the K-T mass extinction measuring extinction a note on killing duration of mass extinctions do mass extinctions differ from background the kill curve. Part 5 Selectivity of extinction: Ice Age Blitzkrieg selectivity of the Blitzkrieg body size and the K-T extinction other examples of bias other examples of selectivity the Trilobites' bad genes some implications summary. Part 6 The search for causes: the rarity of extinction just so stories beware of anthropomorphism! the kill curve revisited. Part 7 Biological causes of extinction: are species and ecosystems fragile? the case of the heath hen importance of the first strike problems of small populations competition species-area effects species-area and past extinctions the great American interchange the history of tropical rain forests. Part 8 Physical causes of extinction: traditional favourites sea level and climate species-area effects testing sea level and climate the Pleistocene experience exotic physical causes unheard-of volcanism cosmic causes. Part 9 Rocks falling out of the sky: cratering rates destructive power Alvarez and the K-T extinction periodicity of extinction and nemesis. Part 10 Could all the extinctions be caused by meteorite impact? plausibility arguments arguments from observation extinctions are linked to craters extinctions are not linked to craters assessment. Part 11 Perspectives on extinction: how to become extinct wanton extinction the role of extinction in evolution bad genes or bad luck? a note on extinctions today. Epilogue: did we choose a safe planet?.

Taxon age and selectivity of extinction

Taxon-age distributions were compiled for families of marine animals surviving or becoming extinct in each stage of the Phanerozoic. I demonstrate, through the use of a modified bootstrap analysis, that there is no difference between the longevity of families becoming extinct during times of background extinction and times of mass extinction. In both mass and background extinction intervals the mean age of families that become extinct is 2 standard deviations below the geometric mean taxon age of families available for extinction. Young families are more susceptible to extinction, perhaps as the result of lower species richness or of occupying a smaller geographic range. There is no tendency during mass extinctions toward loss of families with different taxon ages other than those that become extinct during background times. Thus, in terms of family survival, mass extinction appears to be an exaggeration of processes of background extinction.

Biological Selectivity of Extinction: A Link between Background and Mass Extinction

The phenomenon of non-random or selective survival across major extinction boundaries in the geologic past is poorly understood but increasingly recognized as a critical area for future research. A current hypothesis, developedfrom a comparison of extinction patterns among Late Cretaceous molluscs, is that biological adaptations of organisms effectual during normal times of earth history are ineffectual during times of mass extinction. Microsampling of laminated biosiliceous marine sediments from the highlatitutde Alpha Ridge (-86? N lat.) provides evidence of an actively exploited biological adaptation by Late Cretaceous planktonic diatoms. Distinctive laminae reveal a life-history strategy comprised of alternating planktonic and nonplanktonic stages. Contrary to the hypothesis that mass extinctions are indifferent to biological adaptations, these data indicate a link between selection for traits in normal paleoenvironmental settings and differential survival during an unexpected episode of paleoenvironmental deterioration during a mass extinction. Planktonic diatoms, adapted locally to surviving periods of stress by leaving the plankton environment, may have differentially survived a global crisis at the end of the Cretaceous as a consequence of a life-history trait. The interaction of this proximate biological adaptation and the postulated end-Cretaceous extinction mechanisms may have played a major role in the unexpectedly high survival of planktonic diatoms, documenting a clear example of causal dependency between a biologic character selected for during times of normal or background extinction and macroevolutionary survivorship during times of crisis.